This project will assay the levels of messenger RNA in individual neurons by in situ hybridization and autoradiography. We will study cholinergic and monoaminergic neurons of rodent brain given partial lesions to evaluate if the remaining neurons show compensatory hyperactivity. The effects of age will be studied on compensatory responses. We will examine brains of Alzheimer's patients, obtained post-mortem, for effects on neuronal messenger RNA levels, to examine the hypothesis that gene activity is impaired in Alzheimer's disease. The types of messenger RNA to be measured inclue total poly(A)RNA, calmodulin, beta-tubulin, and enzymes of neurotransmitter synthesis.